Comparison of acid neutralization by chemical weathering between acidifiedand non-acidified watersheds

In eastern Asia, emission of acid materials and acid deposition will increa se with industrialization in future, and freshwaters in Japan are likely to become acidified. In this article, an evaluation method for acid-neutraliz ation by chemical weathering was applied to one acidified watershed in U.S. A. and three non-acidified watersheds in Japan, and effect of hydrogeochemi cal properties on chemical weathering and stream water chemistry was discus sed. In three non-acidified watersheds in Japan, areal chemical weathering rates of primary minerals are much larger than those observed in U.S.A. Wat ersheds in both countries show no difference in mineralogy, while the soil thickness (weathered profile) in watersheds is contrastive between acidifie d and non-acidified watersheds. Therefore, it is concluded that acidity is neutralized by chemical weathering of primary minerals in thick weathered p rofiles in Japanese watershed. In non-acidified Japanese watersheds which h as the smallest acid-neutralization capacity in three observed watersheds, stream water will not acidify even if the acid deposition increases as much as two or three times the observed level. From the viewpoint of Japan's na tionwide streamwater chemistry, more than 90% of the watersheds have far gr eater acid-neutralization capacities than this watershed, and will not be a cidified even in cases where the acid deposition increase as much as two or three fold.